Question

Please explain how you got the answer

Answer 1

The answer is −2y^2 + 9y − 4

I simplified by multiplying -y and 2y, 4 and 2, 2y and 1, and -y and -1 which simplified again is the answer above.

Answer 2

`\bf (-y+4)(2y-1)\implies \stackrel{(-y)(2y-1)}{-2y^2+y}~~+~~\stackrel{(4)(2y-1)}{8y-4}\implies -2y^2+9y-4`

notice, just like in any multiplication, you can simply multiply each term of either polynomial times the other, sum them up and then cancel like-terms.